enabling ip forward

ktang@TangLin:~$ sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 0

ktang@TangLin:~$ sudo vi /etc/sysctl.conf

ktang@TangLin:~$ sudo sysctl -p /etc/sysctl.conf
kernel.printk = 4 4 1 7
kernel.maps_protect = 1
fs.inotify.max_user_watches = 524288
vm.mmap_min_addr = 65536
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.all.rp_filter = 1
net.ipv4.ip_forward = 1

ktang@TangLin:~$ sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 1

Here is a great site of cheap sheet